Field of the Invention
The invention relates to an electromechanical brake booster, comprising a plunger rod for coupling a brake pedal lever to a brake master cylinder, a gear motor, which is coupled with the plunger rod, and a control device, which is connected to the gear motor for the purpose of driving the same.
Description of the Background Art
An electromechanical brake booster is known, for example, from DE 10 2007 032 501 A1. Due to the connection between the brake pedal lever and the brake master cylinder, in contrast to systems using a pedal simulator, the pedal effort applied by the driver may be used to build up braking pressure in the brake master cylinder. Force may be applied with the aid of the electromechanical brake booster both in the direction of the pedal effort and in the opposite direction, for example to support the driver in a braking operation or to assist in the return of the brake pedal lever to its starting position.
Due to friction and hysteresis effects, the return of the brake pedal lever using hydraulic pressure in the brake master cylinder may be slower than desired under certain circumstances. From time to time, the problem also arises that the plunger rod velocity is too high toward the end of the return motion, so that high Bernoulli forces may occur at the end stop for the starting position of the brake pedal lever. This is caused, in particular, by return springs situated in the system, which provide a defined response force in the starting position of the brake pedal lever. A response force of this type is generally felt to be positive for the pedal feel and has a brand-typical and vehicle-typical setting.
In this connection, if a pedal force FP=0 is present at the brake pedal lever, DE 10 2007 032 501 A1 proposes to generate a negative power assist in the brake booster which is directed in the opposite direction to the usual actuation of the brake pedal lever, the negative power assist transitioning to a positive power assist, which assists the pedal force as the pedal force increases. A mechanical return spring within the brake booster may be omitted hereby, or it may be designed to be much softer and be less tightly pretensioned. The lack of force for an optimum response force is actively generated by the brake booster. For this purpose, an assistance characteristic is provided, which predefines the power assist of the brake booster as a function of the detected pedal force FP.